Collectively, these studies show that IDO is a potent immunomodulatory molecule with an important role in the mechanisms determining the pathogenesis of autoimmunity, and suggest that the differential effect of MyD88 and TRIF on Ido expression in DCs exposed to apoptotic cells explains at least in part the differential functions of MyD88 and TRIF in diabetes development. Here, IDO1 is linked to diabetes mellitus.